1. Field of the Invention
The present invention relates to a CPP (Current Perpendicular to the Plane) giant magnetoresistive head in which a sensing current flows in the thickness direction (perpendicularly to the film plane).
2. Description of the Related Art
Giant magnetoresistive (GMR) elements used for hard disk devices and magnetic sensors are roughly divided into a CIP (Current in the Plane) type in which a sensing current flows in parallel with the film plane of each of layers constituting an element, and a CPP (Current Perpendicular to the Plane) type in which a sensing current flows perpendicularly to the film plane of each of the layers constituting an element.
FIG. 55 is a longitudinal sectional view showing the structure of a CPP-GMR head using a conventional CPP-GMR element. A CPP-GMR head 100 comprises a lower shield layer 110 extending in the X direction shown in the drawing, a lower nonmagnetic metal film 120 formed on the lower shield layer 110 at its center in the X direction, and a free magnetic layer 131, a nonmagnetic metallic material layer 132, a pinned magnetic layer 133, an antiferromagnetic layer 134, and an upper nonmagnetic metal film 140, which are laminated on the lower nonmagnetic metal film 120. The CPP-GMR head 100 further comprises an upper shield layer 150 formed over the upper nonmagnetic metal film 140 to extend in the X direction, hard bias layers 163 formed in contact with parts of the free magnetic layer 131 and both sides of the nonmagnetic layer 132, insulating layers 161 filling in the respective spaces between the hard bias layers 163 and the lower shield layers 110, and insulating layers 164 filling in the respective spaces between the hard bias layers 163 and the upper shield layer 150. Furthermore, bias underlying layers 162 are disposed between the hard bias layers 163 and the insulating layers 161.
In the CPP-GMR head having the above-described construction, a sensing current also flows through the antiferromagnetic layer 134 comprising, for example, Pt—Mn. The antiferromagnetic layer 134 has a resistivity of about 200 μΩ·cm which is significantly higher than those of the nonmagnetic metal films 120 and 140, the free magnetic layer 131, and the pinned magnetic layer 133. Also, the antiferromagnetic layer 134 must be thickly formed for maintaining antiferromagnetic characteristics. For example, when the distance between the upper and lower shields is about 600 Å, the thickness of the antiferromagnetic layer 134 is about 200 Å. When the thick antiferromagnetic layer 134 having high resistivity is provided, the antiferromagnetic layer 134 has high resistance and thus generates heat when the sensing current flows therethrough. Since the temperature of the whole of the head is increased by the generated heat (Joule heat), the reliability and high-frequency characteristics of the head deteriorate. Also, the thick antiferromagnetic layer 134 causes a difficulty in decreasing the shield distance between the upper and lower shield layers, thereby causing an disadvantage to increasing the recording density.
Therefore, it has been recently proposed to omit the antiferromagnetic layer 134. However, in order to stabilize magnetization of the pinned magnetic layer 133 without using the antiferromagnetic layer 134, the material used for forming the pinned magnetic layer 133 is greatly limited, and it is thus difficult to improve a change (ΔR·A) in magnetoresistance per unit area. Also, when the magnetization of the pinned magnetic layer 133 is stabilized without using the antiferromagnetic layer 134, the magnetization of the pinned magnetic layer 133 is weakly pinned. Therefore, when the direction of a sensing current magnetic field generated by passing the sensing current is different from the direction of a magnetic moment of the pinned magnetic layer 133, the sensing current magnetic field has the problem of fluctuating the magnetization direction of the pinned magnetic layer 133.
In a CIP-GMR head, only about 10 percent of a sensing current flows through an antiferromagnetic layer, and the sensing current never flows through shield layers, thereby causing none of the above problems.